Content display issue - HTML code formatting ignored & exposed

Drupal 4.7.6
Apache 2.0.54
MySQL 4.1.16
PHP 5.2.1
Client browsers: FF 2.0.0.3, IE 7.0.5730.11

I have a relatively new site up and all is running well except for the fact that any nodes I create fail to put the html tags into effect and simply show them in raw form (in both previewed and published form). No formatting occurs; everything is in one big paragraph without line breaks, paragraphs, bolding, links or images. For the time being, I am just using these tags: <a>, <img>, <strong> and <em>.

I started troubleshooting by looking at my input types to verify that my user has permissions to publish as any input type I wish. This was the case. I should mention that this was my first time bothering to do anything in Input Types (outside of setting permissions).

Next, for the "Full" input type I had assumed that by default it would allow all html tags through, but just for the heck of it I went ahead and checked "HTML Filter" in "Full HTML" anyway. No effect on the problem.

I did not have CCK installed before, but I went ahead and installed it to see if I could get around this, but new content types exhibit the exact same behavior.

That's all I can think of, without taking more drastic measures. I did discover, though, that if I publish the same content using the PHP input type, all is well.

Would welcome suggestions.